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From "Anders Morken (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-1704) Allow more concurrency in the lock manager
Date Tue, 13 Feb 2007 15:44:06 GMT

    [ https://issues.apache.org/jira/browse/DERBY-1704?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12472717

Anders Morken commented on DERBY-1704:

In slightly related work, we've recently done a little testing with a single-record select
load on a trunk patched with DERBY-2107 as well as a port of the patches to split the hash
tables in the lock subsystem that you included here. 

With a separate table and index for each thread (to remove latch contention and lock waits
from the equation) we got an overall throughput increase of about 16% compared to a "single
table for all threads" run (given a cache large enough to maintain the database in-memory),
and found that org.apache.derby.impl.services.cache.Clock.find()/release() caused about 5
times more contention than the synchronization in LockSet.lockObject() and LockSet.unlock().
That might be an indicator of where to apply the next push - and validates the "split hashtable"
approach for this workload. =)

For our part, we're proceeding to hack at latching. =)

> Allow more concurrency in the lock manager
> ------------------------------------------
>                 Key: DERBY-1704
>                 URL: https://issues.apache.org/jira/browse/DERBY-1704
>             Project: Derby
>          Issue Type: Improvement
>          Components: Performance, Services
>    Affects Versions:
>            Reporter: Knut Anders Hatlen
>         Assigned To: Knut Anders Hatlen
>            Priority: Minor
>         Attachments: 1cpu.png, 2cpu.png, 8cpu.png, cleanup1.diff, cleanup1.stat, cleanup1.v2.diff,
cleanup2.diff, cleanup3.diff, cleanup3.stat, split-hashtables.diff, split-hashtables.stat
> I have seen indications of severe monitor contention in SinglePool
> (the current lock manager) when multiple threads access a Derby
> database concurrently. When a thread wants to lock an object, it needs
> to obtain the monitor for both SinglePool and LockSet (both of them
> are global synchronization points). This leads to poor scalability.
> We should investigate how to allow more concurrency in the lock
> manager, and either extend SinglePool or implement a new manager.

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